In recent years, microwave communication systems have been attracting attention as a means of interpolating between optical transmission lines and wireless trunk lines. A microwave transmission system has a wide range of uses such as replacing and backing up a mobile telephone network, inter-building communication, and an optical communication network. Recently, demand for microwave transmission systems as a communication system that connects base stations in the mobile telephone network market, which is rapidly expanding globally, has been greatly extending owing to such characteristics as the economical performance of devices, the ease of construction, the flexibility with respect to system modifications, and the large capacity.
As demand for higher speed and wider area communication increases accompanying the aforementioned, the provision of a lower cost and high-quality line service has been desired. For example, as the complexity of mobile networks increases, a reduction in the CAPEX (capital expenditure) and OPEX (operating expense) of operators is sought. For that reason, an improvement in technology that performs line switching during fault occurrence is absolutely necessary in terms of the economical performance of communication devices. Also, it is necessary to flexibly and dynamically perform monitor/control line switching processing and route change processing between NMSs (network management systems) and NEs (network elements). Therefore, technology for realizing these has conventionally been proposed (refer to Patent Document 1).
In order to dynamically realize the monitor/control line switching processing and route change processing as described above, a monitor/control signal (hereinbelow called an “SV signal”) is used. There are times when communication is performed with the SV signal separated from than the main signal and using a different path in the wired section line between NEs. Also, there are times when communication is performed with the SV signal being multiplexed on the main signal to use the same path in the wired section line between NEs. SV is an abbreviation for Supervisory.